Sugar mixed with water is an important component of cut flower preservation. However, it should not be used by itself. Cut flowers require a certain amount of acidity in their water, as well as bacterial control if they are to thrive. All necessary components exist in commercial flower preservatives, but can also easily be replicated at home.
Sugar is added to water to provide food to cut flowers, thus preserving their lives. Whether it is part of a homemade cut flower preservative recipe or a commercially available flower preservative, sugar is most commonly used in conjunction with water. Other ingredients are usually also included.
Cut flowers should be placed in water with some sort of preservative as soon as possible after cutting. This preserves the flowers at their best, without allowing them time to begin an accelerated period of decay.
Sugar alone mixed with water is not enough to preserve flowers. Regardless of which type of flower it is, cut flowers prefer slightly acidic water. Most water is not acidic enough on its own to satisfy the needs of cut flowers. Ideal water pH for cut flowers is between 3.5 and 4.0 (keep in mind that a pH of 7 is neutral). Commercial preservatives usually include some sort of biocide to address the problem of bacterial growth in water, as well as citric acid to enhance the acidity of the water.
While sugar is a great source of food for cut flowers, it is also a great source of food for bacteria. For this reason, many homemade floral preservative recipes call for bleach or hydrogen peroxide to help control bacterial growth. When flowers are cut, their juices contain sugars and amino acids that bacteria find irresistible. Bacteria do not do well in a dry environment, so their effects are not usually witnessed on a bunch of flowers bought from a florist. Their effects are felt when the cut flowers are immersed in water, where bacteria thrive.
Hydrogen peroxide or bleach should be factors in homemade flower preservative recipes, alongside the sugar. Commercial flower preservative recipes should include some sort of biocide as well to kill bacteria. Additionally, the bottom inch of all cut flower stems should be cut off prior to immersion in any water/plant food formulation. The Department of Environmental Horticulture at the University of California -- Davis has found that cutting a single inch off the bottoms of stems removes virtually all bacteria that were attracted to the cut flowers when they began to ooze juice. However, without combining this practice with an effective biocide in the plant's water, bacteria will thrive once more. Plain sugar water is unfortunately not a good way to achieve healthy, long-lasting cut flowers.